OF-07-06 Geologic Map of the Garo Quadrangle, Park County, Colorado


The purpose of this map is to describe the geologic setting of the 7.5-minute quadrangle. Consulting geologists Robert Kirkham and Karen Houck, field assistant Neil Lindsay, and volunteer Stephen Keller conducted field work for the project during the summer and fall of 2006. Geologic maps produced by the CGS through the STATEMAP program are intended as multi-purpose maps useful for land-use planning, geotechnical engineering, geologic-hazards assessment, mineral-resource development, and ground-water exploration. Digital ZIP/PDF download. OF-07-06D

From the Author’s Notes:

The Garo 7.5-minute quadrangle lies in the western part of South Park, a high-altitude intermontane valley in central Colorado. The map area covers approximately 57 square miles in Park County and is south of the town of Fairplay and west of the town of Hartsel. U.S. Highway 285, Colorado Highway 9, and numerous county-maintained and unimproved public and private roads provide access to most of the quadrangle. The quadrangle is named for the townsite of Garo, which used to be an important stop along the now-abandoned Denver, South Park, and Pacific Railroad (Simmons, 2002).

The foothills of the Mosquito Range are in the western part of the quadrangle. The northwest-southeast-trending ridge in the southeast part of the quadrangle is referred to by the local residents as the Lone Hills. Red Hill, which is a narrow, elongate ridge that extends for tens of miles across South Park, crosses the northeast part of the quadrangle. This ridge is also referred to as the Dakota hogback, because the erosion resistant Dakota Sandstone underlies the hogback ridge. A small part of the western flank of Reinecker Ridge occupies the northeast corner of the quadrangle. Elevations range from a high of about 9,600 feet above mean sea level in the foothills along the western edge of the quadrangle to a low of about 8,900 feet in the southeastern corner of the quadrangle. Except for the foothills of the Mosquito Range and the Lone Hills, most land in the quadrangle slopes gently south or southeast.

Several perennial streams cross the quadrangle. Trout Creek and the Middle Fork of the South Platte River are in the northeast part of the quadrangle. Fourmile Creek, High Creek, and the South Fork of the South Platte River are in the central and western parts of the quadrangle.
For brevity, the two forks of the South Platte River are often called simply the Middle Fork or South Fork. The Middle Fork passes through the Dakota hogback in a water gap near the townsite of Garo.

Most land in the quadrangle is either privately owned, administered by the U.S. Forest Service or Bureau of Land Management, or owned by the Denver Water Department. Most of the latter’s property was recently acquired from the Colorado State Land Board.